Liquid level detection apparatus

ABSTRACT

A liquid level detection apparatus of the present invention includes contacts provided at a distal end portion of a contact plate, and resistance plates which are formed on a wiring board, and have respective conductor portions over which the contacts can slide, respectively, so as to detect a liquid level. Conductor patterns other than the conductor portions are formed on those regions of the wiring board which the contacts at the distal end portion of the contact plate contact during the time when an arm holder is mounted on the wiring board.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a liquid level sensor having a float armswingable in accordance with a liquid level, and more particularly to aliquid level detection apparatus which is suitably mounted on a fueltank of a vehicle using a liquid (such as gasoline or gas oil) as fuel,and detects a residual amount of the fuel.

2. Related Art

A conventional liquid level detection apparatus, having a structureshown in FIGS. 6 to 9, is commonly used (see JP-A-2004-061420 (FIGS. 8to 10)).

As shown in FIG. 6, the conventional liquid detection apparatus 91Acomprises a resin-molded frame 92, a metallic float arm 93, aresin-molded arm holder 94, contact plates 95, a float which hasbuoyancy relative to a liquid to be measured, and is mounted at a distalend portion of the float arm 93, and a circuit board 97 having aresistance plate mounted thereon.

One end portion of the float arm 93 which serves as a rotation shaftportion 93 a is passed through a mounting hole 94 a in the arm holder94, and is rotatably inserted in amounting hole 92 a formed in the frame92.

A distal end portion of the rotation shaft portion 93 a is fitted in anannular projecting portion 96 formed on and projecting downwardly from alower side of the frame 92. The arm holder 94 is mounted on the frame 92so as to rotate or swing around an axis of the rotation shaft portion 93a. The float is mounted on the other end portion (that is, the distalend portion) of the float arm 93.

The contact plates 95, fixed to the arm holder 94, have resiliency, andcontacts 95, provided respectively at distal end portions of the contactplates 95, are urged by the resiliency into contact respectively withconductor portions 97 a (see FIG. 9) mounted on the frame 92.

As shown in FIG. 7, the two contact plates 95 are arranged adjacent toeach other in a forward-rearward direction. The first contact plate 95and the second contact plate 95 are held in contact respectively withthe conductor portions 97 a provided on the circuit board 97.

As shown in FIG. 8, each contact 95 a includes a lower portion 98 of alarger diameter, and an upper portion 99 of a smaller diameter, and anannular groove 100 is formed between the lower portion 98 and the upperportion 99. This annular groove portion 100 is fitted in a hole formedthrough the contact plate 95. A lower surface of the lower portion 98 isadapted to contact the conductor portion 97 a.

The liquid level detection apparatus 91A is mounted on a container orvessel for storing a liquid, and when the float moves upward or downwardin accordance with a change in the liquid level, the float arm 93 isswung around the axis of the mounting hole 92 a within a predeterminedangle range.

In accordance with this swing movement, the contact 95 a on each contactplate 95 slides over the conductor portion 97 a, with its lower portion98 held in sliding contact with the conductor portion 97 a, so that aresistance value between one end of the conductor portion 97 a and thecontact 95 a on the contact plate 95 changes in a sensor circuit (notshown). This resistance change is detected by a sensor circuit, therebyobtaining a level signal representative of the amount of change of theliquid level.

As shown in FIG. 9, in the conventional liquid level detection apparatus91A, when the contact plate 95 is to be mounted on the frame 92, thecontact plate 95 is inserted in a direction of an arrow in FIG. 9. Inthis inserting operation, the contacts 95 a, while rubbing an insertionregion 99 (indicated by hatching in FIG. 9) of the ceramics board, areinserted respectively into predetermined positions.

In the above conventional liquid level detection apparatus 91A, however,when the contact plates 95 are to be mounted on the frame 92, thecontacts, while rubbing the ceramics board, are brought into thepredetermined positions because of the structure of the parts.Generally, each contact 95 a is made of a silver alloy, and is lower inhardness than a ceramics material, and therefore when the contact rubsthe ceramics material, there have been encountered problems that thesurface of the contact takes scratches and that the surface of thecontact reacts with moisture in the air, and is ionized to bedeteriorated (an ion migration phenomenon).

And besides, the scratches on the contact surface temporarily cause acontact failure of the contact, so that the output value becomesunstable. Therefore, the conductor is affected by the contact failure ofthe contact, and an indication of a fuel gauge becomes inaccurate, whichhas invited a problem that the operation of the vehicle on which thefuel gauge is mounted is affected.

SUMMARY OF THE INVENTION

This invention has been made in view of the above problems, and anobject of the invention is to provide a liquid level detection apparatuswhich can provide a simple structure by which contacts are preventedfrom being damaged when mounting a contact plate on a frame, therebypreventing the detection accuracy from being lowered.

1) A liquid level detection apparatus comprising a float arm whichincludes a swing portion for swing around an axis of its rotation shaftportion, and has a float mounted on a distal end portion thereof; an armholder which holds the float arm, and enables the float arm to be swungaround the axis of the rotation shaft portion; a contact plate which isfixed to the arm holder, and is operatively associated with the swingportion of the float arm; a contact provided at a distal end portion ofthe contact plate; and a resistance plate which is formed on a wiringboard, and has a conductor portion over which the contact can slide soas to detect a liquid level; characterized in that a conductor patternformed other than the conductor portion is formed on that region of thewiring board which the contact at the distal end portion of the contactplate contacts during the time when the arm holder is mounted on thewiring board.

In the liquid level detection apparatus of the above construction, theconductor pattern formed other than the first-mentioned conductorportion is formed on part of the wiring board, and with thisconstruction the contact at the distal end portion of the contact plateis prevented from coming into direct contact with the wiring boardduring the mounting of the arm holder on the wiring board. Therefore,the contact will not be damaged or deteriorated by the wiring boardhigher in hardness than the contact, and there can be provided theliquid level detection apparatus of high reliability.

2) In the liquid level detection apparatus, the conductor pattern may beformed along an inserting direction of the contact during the mountingof the arm holder.

The contact can be protected with the simple construction without theneed for effecting a complicated change in the structure.

3) In the liquid level detection apparatus, gaps may be formed in theconductor pattern so that the contact will not come into contact withthe wiring board during the mounting of the arm holder on the wiringboard.

The material for forming the conductor pattern can be saved, and besidesin the event that foreign matters such as dirt are deposited on thecontact during the mounting operation, a foreign matter-removing effectcan be achieved.

In the liquid level detection apparatus of the present invention, theconductor pattern formed other than the conductor portion is formed onthat region of the wiring board which the contact at the distal endportion of the contact plate contacts during the time when the armholder is mounted on the wiring board. Therefore, damage anddeterioration of the contact by contacting engagement are positivelyprevented, and there can be provided the liquid level detectionapparatus of high reliability.

In addition, the conductor pattern is formed along the insertingdirection of the contact during the mounting of the arm holder, andtherefore the contact can be protected with the simple constructionwithout the need for effecting a complicated change in the structure.

Furthermore, the gaps are formed in the conductor pattern so that thecontact will not come into contact with the wiring board during themounting of the arm holder on the wiring board, and therefore thematerial for forming the conductor pattern can be saved, and besides inthe event that foreign matters such as dirt are deposited on the contactduring the mounting operation, the foreign matter-removing effect can beachieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing one preferred embodiment of aliquid level detection apparatus of the present invention;

FIG. 2 is a cross-sectional view of an important portion of the liquidlevel detection apparatus of FIG. 1;

FIG. 3 is a plan view showing a wiring board of the liquid leveldetection apparatus of the invention;

FIG. 4 is a plan view showing a modified wiring board of the liquidlevel detection apparatus of the invention;

FIG. 5 is a plan view showing another modified wiring board of theliquid level detection apparatus of the invention;

FIG. 6 is a cross-sectional view of a conventional liquid leveldetection apparatus;

FIG. 7 is an enlarged view showing contacts of contact plates;

FIG. 8 is an end view of the contact of the contact plate of FIG. 7; and

FIG. 9 is a plan view of a conventional wiring board.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One preferred embodiment of a liquid level detection apparatus of thepresent invention will now be described in detail with reference toFIGS. 1 to 5. FIG. 1 is a perspective view showing one preferredembodiment of the liquid level detection apparatus of the invention,FIG. 2 is a cross-sectional view of an important portion of FIG. 1, andFIGS. 3 to 5 are plan views showing wiring boards, respectively.

As shown in FIG. 1, the liquid level detection apparatus 1 of thisembodiment comprises a frame 2, a metallic float arm 3, an arm holder 4,a contact plate 5, a float 6 having buoyancy relative to a liquid to bemeasured, and the wiring board 7. The frame 2 is provided with anelectric circuit for detecting a liquid level, the electric circuitcomprising, for example, resistance plates 7 a and 7 b and outputterminals 8 which will be described later.

Stoppers 9 a and 9 b are formed respectively at upper and lower edges ofan open side of the frame 2, and each of the stoppers 9 a and 9 b has apredetermined length which is determined in view of the structure of thefloat arm 3.

As shown in FIG. 2, a first bearing portion 2 a is formed at the frame2, and is disposed adjacent to a right end thereof, the first bearingportion 2 a being part of the frame 2. A first bearing portion rotationshaft hole 2 c is formed through the first bearing portion 2 a, and arotation shaft portion 3 a of the float arm 3 is passed through thisrotation shaft hole 2 c. A second bearing portion 2 b is formed at theframe 2, and is disposed beneath the first bearing portion 2 a, and isspaced a predetermined distance from the first bearing portion 2 a ingenerally parallel relation thereto, the second bearing portion 2 bbeing part of the frame 2. A second bearing portion rotation shaft hole2 d is formed through the second bearing portion 2 b, and is opposed tothe first bearing portion rotation shaft hole 2 c. The rotation shaftportion 3 a is rotatably inserted into this rotation shaft hole 2 c.

That portion of the frame, disposed between the first bearing portion 2a and the second bearing portion 2 b, is formed into such a shape that alower holding portion 4 b of the arm holder 4 (described later) can beengaged with this portion. The float arm 3 is in the form of a singlemetallic rod, and includes the rotation shaft portion 3 a serving as theaxis of rotation, and a swing portion 3 b which is bent at generallyright angles relative to the rotation shaft portion 3 a, and isswingable around the axis of the rotation shaft portion 3 a. The float 6of a rectangular parallelepiped shape, having buoyancy relative to theliquid to be measured, is mounted at a distal end portion of the swingportion 3 b of the float arm 3.

The arm holder 4 supports the float arm 3, and is engaged with the frame2 to hold the float arm 3 so as to cause the float arm 3 to be swungaround the axis of the rotation shaft portion 3 a. The arm holder 4 hasa generally U-shaped cross-section, and includes an upper holdingportion 4 a and the lower holding portion 4 b which are generallyparallel to each other. The upper and lower holding portions 4 a and 4 bhold the first bearing portion 2 a of the frame 2 therebetween in theupward and downward direction.

An upper holding portion rotation shaft hole 4 d and a lower holdingportion rotation shaft hole 4 e are formed through the upper holdingportion 4 a and the lower holding portion 4 b, respectively, in such amanner that the two holes 4 d and 4 e are opposed to each other. Therotation shaft portion 3 a of the float arm 3 is rotatably received inthe upper holding portion rotation shaft hole 4 d and the lower holdingportion rotation shaft hole 4 e. Arm holding portions 4 c of a claw-likeshape are formed on an upper surface of the upper holding portion 4 a,and the swing portion 3 b of the float arm 3 can be press-fitted into agap between the two arm holding portions 4 c from the upper side, sothat the arm holding portions 4 c hold the press-fitted swing portion 3b.

The contact plate 5, fixed to the arm holder 4, has resiliency, andcontacts 5 a, provided at a distal end portion of the contact plate 5,are urged by the resiliency into contact respectively with theresistance plates 7 a and 7 b of the wiring board 7 mounted on the frame2. An edge of an inner periphery of the upper holding portion rotationshaft hole 4 d is chamfered, and the diameter of this rotation shafthole 4 d is decreasing gradually downwardly from the upper surface ofthe upper holding portion 4 a such that the diameter of the rotationshaft hole 4 d at the lower surface of the upper holding portion 4 a isgenerally equal to the diameter of the rotation shaft portion 3 a.Therefore, the rotation shaft portion 3 a of the float arm 3 can beeasily passed through the rotation shaft hole 4 d, and the time,required for the assembling operation, is reduced.

Namely, in the assembling operation, the rotation shaft portion 3 a ofthe float arm 3 is passed sequentially through the upper holding portionrotation shaft hole 4 d, the first bearing hole 2 c, the lower holdingportion rotation shaft hole 4 e and the second bearing portion rotationshaft hole 2 d from the upper side. The swing portion 3 b of the floatarm 3 is press-fitted into the gap between the two arm holding portions4 c, and is held by these arm holding portions 4 c.

In this condition, the lower surface of the first bearing portion 2 aand the upper surface of the lower holding portion 4 b abut against eachother, and the withdrawal of the float arm 3 from the frame 2 isprevented by the passage of the rotation shaft portion 3 a through thevarious shaft holes, the holding of the swing portion 3 b by the armholding portions 4 c and the contact of the first bearing portion 2 awith the lower holding portion 4 b.

The above liquid level detection apparatus 1 is mounted on a containeror vessel (not shown) for storing a liquid (such as gasoline) to bemeasured. When the float 6 moves upward or downward in accordance with achange in the liquid level, the float arm 3 is swung around the axis ofthe rotation shaft portion 3 a within a predetermined angle range.

In accordance with this swing movement, the contact 5 a on the contactplate 5 slides over the resistance plate 7 a, and a resistance valuebetween one end of the resistance plate 7 a and the contact 5 a of thecontact plate 5 changes in the detection circuit. This resistance changeis detected, and a level signal representative of the amount of changeof the liquid level can be obtained from the output terminal 8.

As shown in FIG. 3, the wiring board 7 has resistance plates 7 a and 7 b(each having a conductor portion 11) provided thereon, and each contact5 a slides over the corresponding resistance plate 7 a, 7 b so as todetect a liquid level. Conductor patterns 12 a and 12 b other than theconductor portions 11 are formed on those regions of the wiring board 7which the contacts 5 a at the distal end portion of the contact plate 5contact during the time when the arm holder 4 is mounted on the wiringboard 7. The conductor pattern 12 a is formed between the resistanceplate 7 a and the resistance plate 7 b, while the conductor pattern 12 bis formed at that side of the resistance plate 7 b from which thecontacts 5 a are inserted.

The conductor patterns 12 a and 12 b are formed along the insertingdirection of the contacts 5 a during the mounting of the arm holder. Theconductor patterns 12 a and 12 b are in the form of a mesh-like patternformed by a plurality of generally spot-like conductor elements. Thespot-like conductor elements are so sized and spaced from one another sothat the contacts 5 a will not come into direct contact with the wiringboard 7 during the above mounting operation. With this arrangement, theamount of conductor paste used for forming the conductor patterns 12 aand 12 b can be reduced. And besides, in the event that foreign matterssuch as dirt are deposited on the contacts 5 a during the mountingoperation, a foreign matter-removing effect can be achieved.

FIGS. 4 and 5 show other embodiments of the invention which are similarto the embodiment of FIG. 3 except that different conductor patterns 12a and 12 b are used. In FIG. 4, the conductor pattern 12 a, 12 b isformed such that stripe-like gaps in the conductor patterns 12 a, 12 bextend in a direction perpendicular to the inserting direction of thecontacts 5 a. In FIG. 5, the conductor pattern 12 a, 12 b is formed suchthat stripe-like gaps in the conductor pattern 12 a, 12 b extend in adirection parallel to the inserting direction of the contacts 5 a.

Gap width of the gaps formed in the conductor patterns 12 a, 12 b, isset to be smaller than a predetermined width, such that the contacts 5 ado not come into direct contact with the wiring board 7, when the armholder 4 is mounted on the wiring board 7. In other words, the gap widthis substantially smaller than the width of the contacts 5 a.

The liquid level detection apparatus of the present invention is notlimited to the above embodiments, and the material, shape, dimensions,form, disposition, etc., of the conductor patterns are not limited. Theuse of the liquid level detection apparatus of the invention is notlimited to the automobile, and it can be applied, for example, to arailway vehicle, ship, various machine tools and so on.

1. A liquid level detection apparatus comprising: a float arm whichincludes a swing portion for swing around an axis of a rotation shaftportion thereof, and has a float mounted on a distal end portionthereof; an arm holder which holds said float arm, and enables saidfloat arm to be swung around the axis of said rotation shaft portion; acontact plate which is fixed to said arm holder, and is operativelyassociated with said swing portion of said float arm; a contact providedat a distal end portion of said contact plate; and a resistance platewhich is formed on a wiring board, and has a conductor portion overwhich said contact can slide so as to detect a liquid level; wherein aconductor pattern formed other than said conductor portion is formed ona region of said wiring board which said contact at the distal endportion of said contact plate contacts when said arm holder is mountedwith respect to said wiring board.
 2. A liquid level detection apparatusaccording to claim 1, wherein said conductor pattern is formed along aninserting direction of said contact when said arm holder is mounted withrespect to said wiring board.
 3. A liquid level detection apparatusaccording to claim 1, wherein a gap is formed in said conductor patternsuch that said contact does not come into contact with said wiring boardwhen said arm holder is mounted with respect to said wiring board.